1. Field
Embodiments of the present invention relate to a regenerative brake control method of a regenerative brake system using an electronic control brake, which may increase a regenerative brake energy recovery rate of a vehicle via brake hydraulic pressure control under low brake pressure conditions.
2. Description of the Related Art
A regenerative brake system converts a part of kinetic energy of a wheel, emitted in the form of thermal energy during braking, into electric energy using a drive motor mounted to a drive shaft of a vehicle, allowing the energy to be reused for vehicle driving, which results in enhanced fuel economy. Thus, the regenerative brake system may need to maximize a regenerative brake energy recovery rate while achieving vehicle braking stability.
Currently, various regenerative brake systems, such as Electro Hydraulic Brake (EHB) systems, hydraulic booster systems, electronic control brake systems, and the like, are in development or in mass-production.
An Electro Hydraulic Brake (EHB) system detects driver requested brake force using a pedal stroke sensor, and generates required hydraulic brake force, which corresponds to a difference between the driver requested brake force and regenerative brake force, via pressure distribution to front and rear wheels. In the case of a 2-wheel drive (2WD) vehicle, if driver requested brake force is less than the maximum capacity of a drive motor of a vehicle at the initial braking stage, the EHB system maintains non-drive wheels (rear wheels of a Front Wheel Drive (FWD) vehicle or front wheels of a Rear Wheel Drive (RWD) vehicle) at a minimum pressure (about 5 bars), and generates hydraulic brake force using pressure of drive wheels (front wheels of an FWD vehicle or rear wheels of a RWD vehicle). Then, if the driver requested brake force becomes greater than the maximum capacity of the drive motor, the EHB system maintains or reduces the pressure of the drive wheels (front wheels of an FWD vehicle or rear wheels of a RWD vehicle) and increases the pressure of the non-drive wheels (rear wheels of an FWD vehicle or front wheels of a RWD vehicle) to generate hydraulic brake force demanded by a vehicle.
Although the regenerative brake control method using the EHB system may advantageously generate additional regenerative brake force of drive wheels by controlling pressure of non-drive wheels at the initial braking stage, generating regenerative brake force of the drive wheels using hydraulic brake force of the non-drive wheels may cause over-braking of the drive wheels at the initial braking stage under high speed conditions. This may deteriorate braking stability due to wheel slippage, or may necessitate a safety system, such as an Anti-lock Brake System (ABS), which restricts regenerative brake control and consequently, a regenerative brake energy recovery rate.
A hydraulic booster system detects driver requested brake force using a pedal stroke sensor, and generates required hydraulic brake force, which corresponds to a difference between the driver requested brake force and regenerative brake force, via simultaneous pressure control of drive wheels (front wheels of an FWD vehicle or rear wheels of a RWD vehicle) and non-drive wheels (rear wheels of an FWD vehicle or front wheels of a RWD vehicle).
To achieve the driver requested brake force by simultaneously controlling pressure of a drive shaft and a non-drive shaft during braking, the regenerative brake control method using the hydraulic booster system needs to additionally generate regenerative brake force of the drive shaft corresponding to the controlled pressure of the non-drive shaft. In this case, the drive shaft is always affected by the regenerative brake force corresponding to the controlled pressure of the non-drive shaft, thus causing over-braking of drive wheels. This may deteriorate braking stability due to wheel slippage when braking at high speed, or may necessitate a safety system, such as an ABS, which restricts regenerative brake control and consequently, a regenerative brake energy recovery rate, similar to the regenerative brake control method using the EHB system.
In regenerative brake control using an electronic control brake system, only brake pressure of a drive shaft which functions to generate regenerative brake force is controlled, which enables distribution of brake force to front and rear wheels in the same manner as a conventional brake system. In this case, since controlling only brake pressure of the drive shaft is possible if driver requested brake force is less than the maximum capacity of a drive motor of a vehicle (regenerative braking at low brake pressure), maximum regenerative brake force of the vehicle is the level of input brake force of drive wheels at the most, in particular, in a middle or low speed section, which may limit a regenerative brake energy recovery rate.
As described above, electric vehicles and hybrid vehicles using regenerative brake energy may exhibit a limited recovery brake energy recovery rate because brake force is less than the maximum capacity of a drive motor of a vehicle in most situations.